Ecco qui il mio tentativo di traduzione (siete tutti invitati a sistemarlo ).

Dear Terry,

I speak for a group of your Italian fans. Here in Italy only a few of your books have been translated, moreover often the translations aren't up to par with your work and that impaires a more widespread acknowledgement of your works. As if it wasn't enough, often SALANI doesn't give answers to our questions. But we aren't writing you to complain (much).
We're writing you, first of all, to give you our best wishes for your birthday (even if they're belated).

Secondly, we want to make a request. As far as we know there isn't an official Terry Pratchett Italian Fan Club and the books' translations make difficult to catch the subtle humour you use and that makes our reading experience so enjoyable.
Therefore, if you authorize us, we would like to become your Official Italian Fan Club so that we'll be able to become a point of reference for those that want to approach this wonderful world.

Lastly we want to thank you for the wonderful characters, worlds and stories that you gift us with, every time with renewed imagination, genius and that touch of craziness that we like so much.

You can reach us at: www.mondodisco.altervista.org
(email: mondodisco@altervista.org)

Yours:

LEWTON (raphael) alphader@wooow.it
Tuffany (Valentina) adara92@yahoo.it
Angua (Flavia) Angua_13@hotmail.com
fungolo (Marta) fungolo2000@yahoo.it
Cyradis (Daniela) cyradis79@yahoo.it
.....